The present invention relates to a semiconductor device having a memory cell and a sense amplifier, a method of retrieving data, and a microcomputer. More preferably, the present invention relates to a semiconductor device, a method of retrieving data, and a microcomputer suitable for accurately retrieving data at a low voltage without increasing a circuit size.
Recently, the number of electric devices operating at a low voltage has been increased. With the increase in the number of such electric devices, it has been required to operate a memory that is disposed in such electric devices at a power source voltage less than 1.0 V.
However, when the memory cell is operated at a low voltage, a voltage difference in information between “1” and “0” written in the memory cell tends to become minuscule. Accordingly, when the information (“1” or “0”) written in the memory cell is retrieved, it is necessary to accurately determine the voltage difference in the information (“1” or “0”) in a sense amplifier where the voltage of the information is amplified and output.
More specifically, when the power source voltage is 1.0 V, for example, if the information “1” has the voltage between 0.6 V and 1.0 V, and the information “0” has the voltage between 0.0 V and 0.4 V, it is necessary to distinguish between the information “1” and the information “0” by the voltage of 0.2 V (0.6-0.4=0.2). Accordingly, when the sense amplifier does not possess high accuracy, and the memory cell has a large variance, it is difficult to accurately retrieve the information (“1” or “0”) when the memory cell is operated at the low voltage.
In order to solve the problems described above, Patent References No. 1 and No. 2 have disclosed a conventional semiconductor device. FIG. 7 is a schematic diagram showing a configuration of the conventional semiconductor device disclosed in Patent References No. 1 and No. 2.    Patent Reference No. 1: Japanese Patent Publication No. 2008-065966    Patent Reference No. 2: Japanese Patent Publication No. 2008-117510
As shown in FIG. 7, the conventional semiconductor device includes a memory cell array unit 71 and a sense amplifier (SA) 72. In the memory cell array unit 71, pairs of a memory cell A and a memory cell B are provided corresponding to one data (information). When the data is written in the memory cell A, the data is inverted and written in the memory cell B. When the data is retrieved, the sense amplifier 72 retrieves each of the data written in the memory cell A and the memory cell B. Accordingly, it is possible to accurately retrieve the data even if the memory cell A and the memory cell B have a variance due to the operation at the low voltage.
In the conventional semiconductor device disclosed in Patent References No. 1 and No. 2, it is necessary to provide a pair of the memory cell A and the memory cell B relative to one data, thereby making an area of the memory cell array unit 71 double. Further, it is necessary to keep an electrical current flowing through the sense amplifier 72 when the sense amplifier 72 retrieves the data.
In view of the problems described above, an object of the present invention is to provide a semiconductor device capable of solving the problems of the conventional semiconductor device. In the present invention, it is possible to accurately retrieve data during an operation at a low voltage with a fewer number of memory cells, so that it is possible to prevent a circuit scale of the semiconductor device for retrieving the data at the low voltage from increasing.
Further objects and advantages of the invention will be apparent from the following description of the invention.